Nontypable Haemophilus influenzae (NTHi) are causative agents of a large percentage of otitis media seen in children. No currently existing vaccine is effective against NTHi. Anti-OMP antibodies have been shown to be protective against experimental NTHi otitis media in the chinchilla model. A 15 Kd peptidoglycan-associated lipoprotein (PAL) of H. influenzae is conserved among NTHi and has been identified as a vaccine candidate. The gene encoding this protein has been cloned, sequenced, and a form of the protein overexpressed in Escherichia coli at Praxis Biologics. Antibodies directed against the recombinant form of the PAL (rPAL) are biologically active against NTHi. The studies outlined in this proposal would optimize the rPAL construction by oligonucleotide directed mutagenesis to remove extraneous sequences derived from cloning vectors and retain antigenicity and efficient expression. New constructions will be tested for antigenicity, immunogenicity, and biologic activity of antisera elicited and the leading candidate selected. This recombinant protein would then be tested in humans for safety and immunogenicity as a prelude to its possible use as a component in an otitis media vaccine.